The oil pump of the invention has a preferred application in engines for automobiles.
As known, engines for automobiles typically comprise an oil pump configured to pump pressurised oil to lubricate the engine.
FIG. 1 shows a variable displacement oil pump of the prior art, which is wholly indicated with 10. The oil pump 10 comprises a pump body 12 connected to an intake channel 12a and to a delivery channel 12b, a rotor 14 capable of rotating inside the pump body 12 about a rotation axis                and an oscillating stator 22 arranged in an eccentric position around the rotor 14 and capable of moving inside the pump body 12 about a rotation pin 23. The rotor 14 is provided with radial cavities 16 inside which vanes 18 slide, the radially outer ends 20 of vanes 18 contacting the inner surface 21 of the oscillating stator 22 (for the sake of clarity of illustration reference numerals 16, 18 and 22 are associated with only one of the radial cavities and with only one of the vanes shown). The vanes 18, the oscillating stator 22 and the rotor 14 define inside the pump body 12 a plurality of chambers 24 (for the sake of clarity of illustration reference numeral 24 is associated with only one of the chambers shown). Oil is fed into the chambers 24 from the intake channel 12a. Such oil is pressurised due to the decrease of the volume of the chambers 24 upon rotation of the rotor 14. The pressurised oil is then fed through the delivery channel 12b to the parts of the engine that need to be lubricated.        
The displacement of the oil pump 10 is determined by the eccentricity between oscillating stator 22 and rotor 14. Therefore, a variation of the aforementioned eccentricity leads to a variation in the displacement of the oil pump.
The eccentricity between rotor and oscillating stator is determined by the balance between the thrusting action exerted on the oscillating stator 22 by a pressurised fluid (typically oil) fed inside a thrusting chamber 28 defined between the pump body 12 and the oscillating stator 22 and the thrusting action exerted on the oscillating stator 22 by a helical spring 30.
The thrusting chamber 28 is delimited on one side by the rotation pin 23 and, on the opposite side, by a gasket 32.
The Applicant has found that in oil pumps of the type described above there can be, at the rotation pin, leakages of the pressurised oil present inside the thrusting chamber. This is due to the fact that, in order to be able to obtain frictionless movement of the oscillating stator with respect to the rotor, the rotation pin is mounted with clearance in the respective housing seats provided in the oscillating stator and in the pump body. A possible oil leakage at the rotation pin causes the oil pump to malfunction or in any case to operate differently from what is provided for at the design stage. In particular, the oil pump is not able to ensure the flow rate for which it was designed.
The technical problem at the basis of the present invention is to avoid possible oil leakages at the rotation pin of the oscillating stator.
The present invention therefore relates to a variable displacement oil pump in accordance with claim 1.
In particular, the oil pump of the invention comprises a pump body connected to an intake channel and to a delivery channel, a rotor able to rotate inside the pump body about a rotation axis and provided with a plurality of vanes, an oscillating stator arranged in an eccentric position around the rotor and pivoted inside the pump body at a rotation pin, and adjustment means for adjusting the displacement of the oil pump acting on the oscillating stator to displace it with respect to the rotor and position it in at least one predetermined operative position, wherein said adjustment means comprise first thrusting means configured to exert a first thrusting action on a first outer surface portion of the oscillating stator arranged on a substantially opposite side with respect to the rotation pin, and a thrusting chamber defined between the pump body and a second outer surface portion of the oscillating stator arranged between the rotation pin and said first outer surface portion, said thrusting chamber being configured to be filled with a predetermined amount of a pressurised fluid to exert on the oscillating stator a second thrusting action opposite to said first thrusting action and suitable for displacing the oscillating stator to take it into said at least one predetermined operative position, characterised in that the thrusting chamber is defined between two opposite sealing gaskets so as to be fluid-dynamically insulated from the rotation pin and in that it comprises an insulation chamber arranged between said at least one thrusting chamber and the rotation pin and connected to an intake conduit.
Throughout the present description and in the subsequent claims, the expression “fluid-dynamically insulated” is used, with reference to the thrusting chamber, to indicate a condition in which passage of fluid from inside the thrusting chamber towards the outside of the thrusting chamber is substantially prevented.
Throughout the present description and in the subsequent claims, the expression “intake conduit” is used to indicate an area having a pressure lower than that of the insulation chamber, that is suitable for allowing a flow of fluid from the insulation chamber towards such an area.
Advantageously, in the oil pump of the invention the aforementioned sealing gaskets and the suction action which the insulation chamber is subjected to keep the rotation pin insulated from the pressurised fluid fed outside of the oscillating stator, thus avoiding possible leakages of the aforementioned pressurised fluid at the rotation pin.
Advantageously, pressurised fluid is not fed into the insulation chamber. Such an insulation chamber acts both as a structural separation chamber between thrusting chamber and rotation pin and as collection chamber of possible fluid that leakages from the thrusting chamber towards the insulation chamber (due, for example, to damage to a sealing gasket of the thrusting chamber). Such a possible fluid is, however, evacuated from the insulation chamber by suction, preventing it from being able to directly reach the rotation pin.
Preferred features of the variable displacement oil pump according to the invention are recited in the dependent claims. The features of each dependent claim can be used individually or in combination with those recited in the other dependent claims.
Preferably, the intake conduit is connected to the intake channel of the pump.
Alternatively, the intake conduit is connected to a distinct suction pump, or to an area located outside of the pump body and having a pressure lower than that of the insulation chamber.
Preferably, the insulation chamber is defined between the rotation pin and a first gasket of said at least two opposite sealing gaskets and said at least one thrusting chamber is defined between the first gasket and at least one second gasket of said at least two opposite sealing gaskets. The possibility that the pressurised fluid which is in the thrusting chamber leaks into the insulation chamber is thus very remote due to the fact that such chambers are fluid-dynamically insulated from one another by a sealing gasket.
Preferably, the first gasket is angularly spaced from the rotation pin by an angle lower than 90° with reference to said rotation axis.
Preferably, the second gasket is angularly spaced from the first gasket by an angle greater than 90° with reference to said rotation axis.
In further embodiments of the oil pump of the present invention, said at least one thrusting chamber comprises a first thrusting chamber arranged between the first gasket and a further sealing gasket arranged between the first gasket and the second gasket, and at least one second thrusting chamber arranged between said further gasket and the second gasket, wherein said first and second thrusting chambers are each configured to be filled, simultaneously or alternatively, with a respective predetermined amount of pressurised fluid.
Preferably, said at least two opposite sealing gaskets are housed in respective seats formed in the oscillating stator.
In an alternative embodiment of the oil pump of the invention, one of said two opposite sealing gaskets is arranged at the rotation pin. In such an embodiment therefore, it is not provided any insulation chamber or any structural separation between rotation pin and thrusting chamber. In this case, leakage of the pressurised fluid at the rotation pin is prevented by the fact that a sealing gasket is arranged in the housing seat of the rotation pin.
Preferably, in all of the aforementioned embodiments, the aforementioned first thrusting means comprises an elastic element, more preferably a helical compression spring. Alternatively, the aforementioned first thrusting means can comprise a thrusting chamber filled by a pressurised fluid.